Surgery can be used to reshape the cornea of the eye to correct for myopia, hyperopia and presbiopia. One method of correcting for such conditions is to use a laser to reshape the surface of the cornea to change the focal length of the lens and thereby compensate for the effects of myopia and hyperopia.
In another procedure, the contour of the surface of the eye can be changed by the insertion of a ring in the stroma of the cornea. The diameter of the ring is thereafter adjusted such that the ring applies pressure to cause the cornea to become flatter and thereby compensate for myopia, or to become more curved and thereby compensate for hyperopia. This procedure is discussed at length in Kilmer, U.S. Pat. No. 5,505,722, dated Apr. 9, 1996. Kilmer discloses a ring which is inserted within the stroma of the cornea of the eye using a cutting tool configured as a coil. The cutting tool is inserted into the cornea of the eye through one or more incisions formed by a marking and cutting tool disclosed by Kilmar.
The annular insert disclosed by Kilmer must be installed through an incision in the surface of the eye. Presently, the installation is made by use of a device of the type disclosed in the Kilmer reference. The device includes a knife having an elongate blade with sharpened edges on the opposing sides of the blade.
It has been found that a problem occurs when an existing knife is used in making the initial cut prior to the installing of such a ring. Specifically, when a patient makes an eye movement just as the surgeon is plunging the blade downward through the cornea of the eye, the movement of the eye causes an excessively long installation cut. The usual consequence of this problem is that the surgery is aborted. It would, therefore, be desirable to provide a knife useable for making the installation cut required for inserting a deforming ring in accordance with Kilmer, U.S. Pat. No. 5,505,722, which will not cause the cut to be enlarged as the result of movement of the eye of a patient.